On-chip leakage current modeling and measurement circuit

ABSTRACT

At least one N-type transistor and at least one P-type transistor separate from the digital circuit are sized to represent the total area of the corresponding type transistors in the digital circuit. The gates of the N-type transistor and P-type transistors are set to voltages according to the corresponding off-state logic levels of the digital circuit. The N-type and P-type transistors form a portion of corresponding current mirror circuits, which can provide outputs to a leakage current monitor and/or a control circuit such as a comparator that determines when leakage current for the N-type or P-type devices has exceeded a threshold. The output of the measurement/control circuit can be used to determine a temperature of and/or control operation of the digital circuit or the system environment of the integrated circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to design characterization methods andcircuits, and more particularly to integrated circuits having on-chipleakage current monitors, such as leakage current estimation ormeasurement circuits.

2. Description of Related Art

In very large-scale integrated circuits (VLSI) such as semiconductormemories and microprocessors, accurate leakage current measurement istypically not possible, since measurement of true leakage currentrequires that all of the devices under measurement be in an “off” state,which generally cannot be commanded at the same time across an entireintegrated circuit die. Further, even if all leakage current paths havean “off” device (e.g., a CMOS circuit in a static state), both “off”devices and “on” devices vary in type and strength across the die.Leakage current across a die is difficult to model, and any model willdeviate substantially from actual leakage current, as the combination oflocal variation with variation of the design values combinessignificantly, particularly in present-day low voltage technologies, inwhich the power supply voltages are decreasing to below one volt.

If a truly accurate leakage current monitor circuit were available,leakage current could be characterized across a circuit design on a die,individual device types could be characterized for leakage acrossvoltage and temperature variations, and used to inform design decisionsand monitor processes. A more accurate temperature monitoring functioncould also be provided, since device leakage can be used as an indicatorof device temperature. Device leakage forms the basis for manytemperature monitoring circuit designs, in which one or more referencedevices conducts a temperature-dependent “off” state current, which ismeasured to generate a temperature analog. Further, leakage currentvalues could be used as a control mechanism for maintaining energy usebelow a predetermined threshold, or for other purposes such as thermalcontrol.

Present leakage current monitoring circuits typically measure a leakageof one or more devices to estimate total leakage of a device, but arenot typically statistically representative of an integrated circuitdesign as a whole, with the exception of actual total device leakagecurrent measurements, which can only provide measurement of the currentconsumed by an integrated circuit while the internal circuits are in asuspended state. Even in a suspended state, all devices are typicallynot in their “off” state, as noted above, and there is no ability todistinguish between leakage of different device types. Other test andmeasurement circuits may be provided to make leakage currentmeasurements and/or model device current leakage, but also fail toprovide a measure of true off-state leakage and fail to provide a modelsufficiently accurate to the describe the actual integrated circuit.

Therefore, it would be desirable to provide methods, circuits andsystems for leakage current monitoring that provide a measure of thetrue off-state leakage current for an integrated circuit design andprovide an accurate, statistically descriptive measure of leakagecurrent within the actual circuit being monitored. It would further bedesirable to provide an accurate temperature monitor in an integratedcircuit. It would be also be desirable to provide such a circuit thatcan provide an accurate leakage current value while the circuit beingmonitored is in an active operating state, and optionally control anenvironment and/or internal operation of the integrated circuit usingleakage current monitoring results.

BRIEF SUMMARY OF THE INVENTION

Accurate monitoring of integrated circuit leakage current and/ortemperature, is provided in a leakage current monitor circuit, a methodof leakage current monitoring, and a system including a leakage currentmonitor. The monitor circuit provides a statistically representativeanalog of the true off-state leakage of one or more circuits, by usingmonitor transistors that have characteristics that represent deviceswithin the circuit(s) for which leakage current is being monitored.

The leakage current monitor circuit is integrated on a die and includesat least one P-type monitor transistor, sized to represent a totality ofthe P-type transistors in a digital circuit being monitored, which isalso integrated on the die. At least one N-type monitor transistor isalso included in the leakage current monitor circuit, which is sized torepresent a totality of the N-type transistors in the digital circuitbeing monitored, and both the P-type and N-type monitor transistors havegate connections set to a voltage that is substantially equal to theircorresponding off-state logic level. In an alternative embodiment of theinvention, only the leakage current/temperature monitor circuit isintegrated on a die and is used to model the leakage current of anintegrated circuit design in a test configuration, and multiple leakagecurrent monitor circuits can be integrated on a single die to evaluateleakage current of a large number of alternative circuit designs. Forexample, a monitor may be assigned for each of several functionalblocks, such as a memory array leakage current monitor and a logic blockleakage current monitor, or multiple leakage current monitors may beprovided to monitor leakage current for regions of a die, providing ageometrical map of leakage current.

A current mirroring circuit can be included within the leakage currentmonitor circuit and integrated on the die, to provide a monitor output,and may be amplified. The monitor output may be provided at a test pador output pin, and/or internal comparison circuits can be provided forcontrolling operation of the digital circuit being monitored or asystem, in which the digital circuit is integrated, and/or to provide atemperature monitoring function. The output of the comparison circuitmay also be accessible to the system or to another test system via atest port, internal register or other suitable interface to informdesign decisions.

The foregoing and other objectives, features, and advantages of theinvention will be apparent from the following, more particular,description of the preferred embodiment of the invention, as illustratedin the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives, and advantages thereof,will best be understood by reference to the following detaileddescription of the invention when read in conjunction with theaccompanying Figures, wherein like reference numerals indicate likecomponents, and:

FIG. 1 is a block diagram of an integrated circuit 10 according to anembodiment of the present invention.

FIGS. 2A-2B are schematic diagrams of leakage current monitor circuitsthat may be used to implement leakage current monitor blocks 14A and14B, respectively, within integrated circuit 10 of FIG. 1 according toan embodiment of the present invention.

FIGS. 3A-3C are block diagrams of leakage current evaluation circuits inaccordance with embodiments of the present invention are performed.

FIG. 4 is a pictorial diagram of a wafer test and design workstationcomputer system in which methods in accordance with embodiments of thepresent invention are performed.

FIG. 5 is a flow chart of a leakage current monitoring method inaccordance with an embodiment of the present invention.

FIG. 6 is a flow chart of a leakage current monitor circuit designmethod in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a leakage current monitor circuitintegrated on a die, methodologies for determining true off-statecurrent leakage of a separate functional digital circuit integrated onthe die, and systems using are such a leakage current monitor circuit tomonitor and/or control the operating conditions of the digital circuit,as well as to evaluate a design of the integrated circuit. The presentinvention also encompasses methodologies for designing such a monitorcircuit. The leakage current monitor circuit has both N-type and P-typetransistors sized to represent the aggregated area of all of the N-typeand P-type transistors in the digital circuit, and may include multipleN-type and P-type transistors sized according to an aggregated area ofclasses of the N-type and P-type transistors having differing thresholdvoltages.

Referring now to FIG. 1, an integrated circuit 10 in accordance with anembodiment of the present invention is shown. Functional circuits 12include one or more functional digital circuit block that provide theoperational functions associated with integrated circuit 10. A separateNFET leakage monitor circuit 14A and PFET leakage monitor circuit 14Bare provided on the same die as functional circuits 12, or optionallymay be located in the kerf area outside of the singulated die region inimplementations for which leakage current monitoring is only providedfor manufacturing evaluation. A decision block and/or test interfacecircuit 16 is provided to evaluate the outputs of NFET leakage monitorcircuit 14A and PFET leakage monitor circuit 14B in order to use theleakage current values for either real-time monitoring and control offunctional circuits 12 and/or an environment provided to integratedcircuit 10 (e.g., power supply voltage and/or operating frequency), orfor manufacturing evaluation purposes in which the leakage currentresults can be reported through a test interface, such as a scan logicinterface to provide useful evaluation results for adjusting the designof functional circuits 12 or evaluating a process used to manufactureintegrated circuit 10. An integrated circuit including a leakage monitorcircuit according to the present invention may, therefore, be used as adesign/process evaluation tool, a real-time operating condition monitor,or may provide a combination of both functions.

Within functional circuits 12, pluralities of N-type transistors N_(VT1)having a first threshold voltage value, N-type transistors N_(VT2)having a second threshold voltage value, P-type transistors P_(VT1)having a third threshold voltage value and P-type transistors P_(VT2)having a second threshold voltage value are illustrated. TransistorsN_(VT1), N_(VT2), P_(VT1), and P_(VT2) implement the digital circuitswithin functional circuits 12 and it is the leakage of those transistorsthat NEET leakage monitor circuit 14A and PFET leakage monitor circuit14B are designed to monitor without affecting the performance offunctional circuits 12 and while providing a true off-state leakagecurrent value that cannot be obtained by directly measuring currentconsumed by functional circuits 12, since at least some of thetransistors within functional circuits 12 will always have gates biasedto a voltage corresponding to an “on” state. For example, in a CMOSdigital circuit having no special provisions for separately controllingthe gates of internal transistors, 50% of the transistors will be biasedto an off-state and the remaining 50% will be biased to an on-state.Even though such a circuit in a static state can be considered“disabled”; since CMOS circuits are only active during switching,measurement of the power supply current passing through the circuit isnot a measurement of true leakage current, since some of the transistorsare on.

In order to determine true leakage current values for transistorsN_(VT1), N_(VT2), P_(VT1), and P_(VT2) in functional circuits 12, NFETleakage monitor circuit 14A includes NFET monitor transistors N_(VTM1)and N_(VTM2), corresponding to transistors N_(VT1) and N_(VT2). PFETleakage monitor circuit 14B includes PFET monitor transistors P_(VTM1)and P_(VT2), corresponding to transistors P_(VT1) and P_(VT2). Monitortransistor N_(VTM1) has a threshold voltage equal to that of transistorsN_(VT1) and has a device area sized in proportion to a nominal totaldevice area of transistors N_(VT1), which may be determined according tonominal design values, a statistical simulation of process variationacross integrated circuit 10, or collected manufacturing data forintegrated circuit 10. The size is generally greatly reduced inproportion, such that leakage current measured through monitortransistor N_(VTM1) is negligible with respect to the actual leakagecurrent passing through transistor N_(VT1) so that leakage currentintroduced by NFET leakage monitor circuit 14A is negligible forreal-time leakage current monitoring applications. Similarly, monitortransistors N_(VTM2), P_(VTM1) and P_(VTM2) have device areas andthreshold voltage corresponding to groups of transistors N_(VT2),P_(VT1) and P_(VT2), respectively, so that the types of transistorsincluded in functional circuits 12 are represented in the leakagecurrent determinations. While the number of transistor types illustratednumber four (two threshold voltage values by two transistordopant/polarity types), it is understood that any number of groups oftransistors according to type within functional circuits 12 can berepresented by similar/identical transistors within NFET leakage monitorcircuit 14A and PFET leakage monitor circuit 14B, so that the leakagecurrent determinations accurately represent the actual devices infunctional circuits 12. Further, more than one transistor for each typemay be included within NFET leakage monitor circuit 14A and PFET leakagemonitor circuit 14B, providing for easy design adjustment of a design ofNFET leakage monitor circuit 14A and PFET leakage monitor circuit 14Busing fingering techniques, for example Leakage current distributionaverages may be obtained for each of the device types, and may also beobtained by region or by functional circuit type by implementingmultiple leakage current monitors for different circuits and/or fordistribution across the die.

Referring now to FIG. 2A, details of NFET leakage monitor circuit 14Aare shown. A current source, provided by transistor P1, supplies currentto monitor transistors N_(VTM1)-N_(VTM5), which represent aggregateN-channel transistor device areas in functional circuits 12 of FIG. 1,according to different threshold voltage types of transistor, and in thecase of monitor transistors N_(VTM4) and N_(VTM5), a “stacked”transistor configuration as may occur in functional circuits 12 whenfoot devices, power control circuits, tri-state buffers, and the likeare present. As noted above, the current through monitor transistorsN_(VTM1)-N_(VTM5) is a statistically representative analog of the trueleakage current through the N-channel devices in functional circuits 12,because the device areas of monitor transistors N_(VTM1)-N_(VTM5) areproportionally representative of the device areas of the actualN-channel transistors within functional circuits 12, according to thethreshold voltage type and/or stacking configurations of the actualN-channel transistors, and further because the gates of monitortransistors N_(VTM1)-N_(VTM5) are biased at the power supply railvoltage corresponding to the logical off state for N-channel transistorsin the functional circuits 12, i.e., ground in the illustratedembodiment. The current source provided by transistor P1 is one branchof a current mirror additionally provided by transistor P2, whichsources an identical current to a differential amplifier formed bytransistors N1, N2 and resistor R1. The output of the differentialamplifier is supplied to a comparison circuit 16A, which includes acomparator formed by transistors N3-N5 and P3-P4. A voltage sourceV_(b1) sets the operating point (gain) of comparison circuit 16A and areference voltage source V_(b2) provides the comparison threshold towhich the output of the differential amplifier formed by transistors N1,N2 and resistor R1 is compared.

Referring now to FIG. 2B, details of PFET leakage monitor circuit 14Bare shown. PFET leakage monitor circuit 14B is similar to NFET leakagemonitor circuit 14A, with a change in polarity type of monitortransistors P_(VTM1)-P_(VTM5), which represent aggregate P-channeltransistor device areas in functional circuits 12 of FIG. 1, accordingto different threshold voltage types of transistor, and in the case oftransistors P_(VTM4) and P_(VTM5), a “stacked” transistor configuration.As noted above, the current through monitor transistorsP_(VTM1)-P_(VTM5) is a statistically representative analog of the trueleakage current through the P-channel devices in functional circuits 12,because the device areas of transistors monitor P_(VTM1)-P_(VTM5) areproportionally representative of the device areas of the actualP-channel transistors within functional circuits 12, according to thethreshold voltage type and/or stacking configurations. A current sourceprovided by transistor N11 and shunted by leakage through transistorsP_(VTM1)-P_(VTM5) is one branch of a current mirror additionallyprovided by transistor N12, which sources an identical current to adifferential amplifier formed by transistors P11, P12 and resistor R11.The output of the differential amplifier is supplied to a comparisoncircuit 16B, which includes a comparator formed by transistors N13-N15and P13-P14. A voltage source V_(b3) sets the operating point (gain) ofcomparison circuit 16A and a reference voltage source V_(b4) providesthe comparison threshold to which the output of the differentialamplifier formed by transistors P11, P12 and resistor R11 is compared.By changing the relative values of voltage sources V_(b1), V_(b2),V_(b3) and V_(b4), the thresholds and relative gains with respect toN-channel and P-channel leakage can be adjusted, so that the results canbe combined to provide a single leakage current monitoring or controlvalue as will be described in detail below. Alternatively, individualcontrols or monitor values can be provided using just the values ofN-channel and P-channel leakage as provided by NFET leakage monitor 14Aand PFET leakage monitor 14B or the outputs of comparison circuits 16Aand 16B.

Referring now to FIGS. 3A-3C, various combining/evaluation circuits asmay be used within decision block and/or test interface 16 of FIG. 1 areshown. FIG. 3A illustrates a comparison-first scheme that combines theoutputs of comparison circuits 16A, 16B, which compare individually, theoutputs of NFET leakage monitor circuit 14A and PFET leakage monitorcircuit 14B as illustrated above; using a weighted decision block 18A.Weighted decision block 18A weights the outputs of comparison circuits16A, 16B according to constants k1 and k2 to yield a control value ormonitor value that can be used to adjust the operation or environment offunctional circuits 12, for example to disable circuits/functionality orreduce power supply voltage/frequency when the output of weighteddecision block 18A exceeds a threshold, or to provide a single factoroutput that can be used, for example to evaluate individual dies in amanufacturing process. The weighting constants, e.g., k1 and k2 can bedetermined in proportion to design statistics for a given design.

FIG. 3B illustrates a different scheme in which weighting factors k1 andk2 are applied by amplifiers 17A and 17B and the resulting valuescombined by a summing circuit 19 before comparison with a predeterminedthreshold using a comparator 16C. FIG. 3C illustrates a further schemethat includes all of the elements of FIG. 3B and weights a decisionbased on the output of comparator 16C according to a factor k3 andanother metric, determined by another metric monitor 20, as compared toa threshold by a comparator 16D and weighted by a factor k4. All of theabove techniques are illustrative techniques for combining the outputsof NFET leakage monitor circuit 14A and PFET leakage monitor circuit 14Bto provide examples of how the true leakage values obtained by thepresent invention may be used, and should not be construed as limitingthe possible ways of combining or using alone, the outputs of NFETleakage monitor circuit 14A and PFET leakage monitor circuit 14B ascontrol variable and/or manufacturing/design evaluation tools.

Referring now to FIG. 4, a system in which methods according toembodiments of the invention are performed, is shown. A wafer tester 40includes a scan unit 41 for providing stimulus to a die 42A on a waferunder test 42, via a probe head 43 having electrical test connections todie 42A. Wafer tester 40 also includes a programmable voltage supply(PVS) 32, which may be used to vary the supply voltage provided tointegrated circuit 10 on die 42A in order to study leakage current vs.supply voltage. PVS 32 is coupled to die 42A via probe head 43. A highspeed interface 30 is included to read information from decisionblock/test interface 16 of integrated circuit.

A workstation computer 48, having a processor 46 coupled to a memory 47,for executing program instructions from memory 47, wherein the programinstructions include program instructions for executing one or moremethods in accordance with an embodiment of the present invention, iscoupled to wafer tester 40, whereby the monitoring described above isperformed and leakage current monitor values are collected and stored inmemory 47 and/or other media storage such as a hard disk. A CD-ROM drive45 provides for import of program instructions in accordance withembodiments of the present invention that are stored on media such ascompact disc CD. Workstation computer 48 is also coupled to a graphicaldisplay 49 for displaying program output values such as the leakagemonitor values or comparison results, as well as design informationconcerning the transistor types and digital circuit device areas thatare used to determine the device areas of the transistors in leakagecurrent monitors 14A and 14B. Workstation computer 48 alone, withoutwafer tester 40 may be used to design suitable leakage current monitorsfrom design data from an integrated circuit, and in particular, inembodiments in which the leakage current monitoring results are used forcontrol, wafer tester 40 is not needed, nor is any other data receivingsystem needed to practice the invention, as the leakage current resultsmay be used only internal to integrated circuit 10 in some embodimentsof the invention. Workstation computer 48 is further coupled to inputdevices such as a mouse 44B and a keyboard 44A for receiving user input.Workstation computer may be coupled to a public network such as theInternet, or may be a private network such as the various “intra-nets”and software containing program instructions embodying methods inaccordance with embodiments of the present invention may be located onremote computers or locally within workstation computer 48. Further,workstation computer 48 may be coupled to wafer tester 40 by such anetwork connection.

Referring now to FIG. 5, a method of leakage current monitoring inaccordance with an embodiment of the present invention is shown. Leakagethrough N-channel transistors in a digital circuit are determined on-dieusing a leakage current monitor that is statistically descriptive of theN-channel transistors in the digital circuit (step 50). Leakage throughP-channel transistors in a digital circuit are determined on-die using aleakage current monitor that is statistically descriptive of theN-channel transistors in the digital circuit (step 52). The leakagecurrent monitor values are optionally combined (step 54) and if theleakage value(s) exceed a threshold (decision 58), circuit operatingparameters (e.g., power supply voltage or frequency, power managementstate, etc.) are adjusted, or for design evaluation purposes, theresults of the leakage current monitoring are displayed (step 60). Untilthe monitoring cycle is ended, or in control schemes, the integratedcircuit is powered-down (decision 62), steps 50-60 are repeated.

Referring now to FIG. 6, a method of designing a leakage current monitorin accordance with an embodiment of the present invention is shown.Aggregate device areas of N-channel transistors in a digital circuit aregathered for each threshold voltage type of N-channel transistor (step70). Aggregate device areas of P-channel transistors in a digitalcircuit are gathered for each threshold voltage type of P-channeltransistor (step 72). Then, the leakage current monitor is designedusing transistors for each N-channel threshold voltage type and eachP-channel threshold voltage type having areas set according to theaggregated device areas for those types of transistors.

While the invention has been particularly shown and described withreference to the preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in form,and details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method for determining leakage current in adigital circuit integrated on a die, the method comprising: firstproviding, on the die and separate from the digital circuit, a firstleakage monitor comprising at least one N-type transistor connected to afirst branch of a first current mirror, the at least one N-typetransistor corresponding to an off state for a first plurality of N-typetransistors in the digital circuit, wherein the first leakage monitorfurther comprises a first differential amplifier connected to a secondbranch of the first current mirror such that current through the secondbranch of the first current mirror mirrors current through the at leastone N-type transistor, the first differential amplifier generates afirst leakage current value; second providing, on the die and separatefrom the digital circuit, a second leakage monitor comprising at leastone P-type transistor connected to a first branch of a second currentmirror, the at least one P-type transistor corresponding to an off statefor a second plurality of P-type transistors in the digital circuit,wherein the second leakage monitor further comprises a seconddifferential amplifier connected to a second branch of the secondcurrent mirror such that current through the second branch of the secondcurrent mirror mirrors current through the at least one P-typetransistor, wherein the second differential amplifier generates a secondleakage current value; and measuring the first leakage current value andthe second leakage current value to determine a leakage current resultbased on the first leakage value and the second leakage current value.2. The method of claim 1, further comprising combining the first leakagecurrent value of the first leakage monitor with the second leakagecurrent value of the second leakage monitor to form a total leakagecurrent value through a common circuit node.
 3. The method of claim 1,further comprising comparing the total leakage current value to apredetermined threshold to yield a leakage current decision value. 4.The method of claim 1, further comprising: first comparing the firstleakage current value with a first predetermined threshold; secondcomparing the second leakage current value with a second predeterminedthreshold; and combining a result of the first comparing and the secondcomparing to form a leakage current decision value.
 5. The method ofclaim 1, wherein the first providing provides a third plurality ofN-type transistors as the at least one N-type transistor, and whereinthe third plurality at N-type transistors have differing correspondingmultiple threshold voltage values and areas, wherein the differingcorresponding multiple threshold voltage values correspond to thresholdvoltage types in the third plurality of N-type transistors in thedigital circuit, and wherein the differing corresponding areas aredetermined according to a total area of the third plurality of N-typetransistors in the digital circuit having the corresponding thresholdvoltage type, and wherein the second providing provides a fourthplurality of P-type transistors as the at least one P-type transistor,and wherein the fourth plurality of P-type transistors have differingcorresponding multiple threshold voltage values and areas, wherein thediffering corresponding multiple threshold voltage values correspond tothreshold voltage types in the fourth plurality of P-type transistors inthe digital circuit, and wherein the differing corresponding areas aredetermined according to a total area of the fourth plurality of P-typetransistors in the digital circuit having the corresponding thresholdvoltage type.
 6. The method of claim 1, further comprising determining anominal temperature of the digital circuit from the leakage currentresult.
 7. The method of claim 1, further comprising adjusting anenvironmental operating parameter of the digital circuit in conformitywith the leakage current result.
 8. An integrated circuit, comprising: adigital circuit configured to provide a functionality of the integratedcircuit; a first leakage monitor comprising at least one N-typetransistor connected to a first branch of a first current mirror, the atleast one N-type transistor corresponding to an off state for a firstplurality of N-type transistors in the digital circuit, wherein thefirst leakage monitor further comprises a first differential amplifierconnected to a second branch of the first current mirror such thatcurrent through the second branch of the first current mirror mirrorscurrent through the at least one N-type transistor, wherein the firstdifferential amplifier generates a first leakage current value; secondleakage monitor comprising at least one P-type transistor connected to afirst branch of a second current mirror, the at least one P-typetransistor corresponding to an off state for a second plurality ofP-type transistors in the digital circuit, wherein the second leakagemonitor further comprises a second differential amplifier connected to asecond branch of the second current mirror such that current through thesecond branch of the second current mirror mirrors current through theat least one P-type transistor, wherein the second differentialamplifier generates a second leakage current value; and a measurementcircuit configured to measure the first leakage current value and thesecond leakage current value to determine a leakage current result basedon the first leakage current value and the second leakage current value.9. The integrated circuit of claim 8, wherein the measurement circuitcomprises a summing circuit for combining the first leakage currentvalue and the second leakage current value, wherein an output of thesumming circuit provides a measurement result corresponding to theleakage current of the totality of the first plurality of N-typetransistors and the second plurality of P-type transistors in thedigital circuit.
 10. The integrated circuit of claim 9, wherein themeasurement circuit further comprises a comparison circuit for comparingthe output of the summing circuit to a predetermined threshold toprovide an indication that the leakage current of the totality of thefirst plurality of N-type transistors and the second plurality of P-typetransistors in the digital circuit exceeds a pre-set value.
 11. Theintegrated circuit of claim 8, wherein the measurement circuitcomprises: a first current sensing circuit for measuring a first leakagecurrent at a source terminal of the at least one N-type transistor; anda second current sensing circuit for measuring a second leakage currentat a source terminal of the at least one P-type transistor, wherein thefirst leakage current and the second leakage current are separatelymeasured by the measurement circuit.
 12. The integrated circuit of claim11, wherein the measurement circuit further comprises: a firstcomparison circuit configured to compare an output of the first currentsensing circuit to a first predetermined threshold; at second comparisoncircuit configured to compare an output of the second current sensingcircuit to a second predetermined threshold; and a combining circuitconfigured to combining a result of the first comparison circuit and theresult of the second comparison circuit to form a leakage currentdecision value.
 13. The integrated circuit of claim 8, wherein the atleast one N-type transistor comprises a third plurality of N-typetransistors, and wherein the third plurality of N-type transistors havediffering corresponding multiple threshold voltage values and areas,wherein the differing corresponding multiple threshold voltage valuescorrespond to threshold voltage types in the third plurality of N-typetransistors in the digital circuit, and wherein the differingcorresponding areas are determined according to a total area of thethird plurality of N-type transistors in the digital circuit having thecorresponding threshold voltage type, and wherein the at least oneP-type transistor comprises a fourth plurality of P-type transistors,and wherein the fourth plurality of P-type transistors have differingcorresponding multiple threshold voltage values and areas, wherein thediffering corresponding multiple threshold voltage values correspond tothreshold voltage types in the fourth plurality of P-type transistors inthe digital circuit, and wherein the differing corresponding areas aredetermined according to a total area of the fourth plurality of P-typetransistors in the digital circuit having the corresponding thresholdvoltage type.
 14. The integrated circuit of claim 8, wherein themeasurement circuit is coupled to the digital circuit for controllingoperation of the digital circuit in conformity with the first leakagecurrent value and the second leakage current value.
 15. The integratedcircuit of claim 8, further comprising an interface coupled to an outputof the measurement circuit to provide information determined inconformity with the first leakage current value and the second leakagecurrent value to an external system.
 16. A method of designing anintegrated circuit having at least one integrated leakage currentmonitor, comprising: determining a design of a functional digitalcircuit within the integrated circuit; first aggregating first totaldevice areas for at least one class of N-type transistor withinfunctional circuit; second aggregating second total device areas for atleast one class of P-type transistor within the functional digitalcircuit; determining a design of a leakage current monitor circuitwithin the integrated wherein a device area of at least one N-typetransistor the generating a current measurement input is set inconformity with a result of the first aggregating, and wherein a devicearea of at least one P-type transistor for generating a currentmeasurement input is set in conformity with a result of the firstaggregating; first providing, on the die and separate horn the digitalcircuit, a first leakage monitor comprising the at least one N-typetransistor connected to a first branch of a first current mirror, the atleast one N-type transistor corresponding to an off state for a firstplurality of N-type transistors in the digital circuit, wherein thefirst leakage monitor further comprises a first differential amplifierconnected to a second branch of the first current mirror such thatcurrent through the second branch of the first current mirror mirrorscurrent through the at least one N-type transistor, wherein the firstdifferential amplifier generates a first leakage current value; andsecond providing, on the die and separate from the digital circuit, asecond leakage monitor comprising the at least one P-type transistorconnected to a first branch of a second current mirror, the at least oneP-type transistor corresponding to an off state for a second pluralityof P-type transistors in the digital circuit, wherein the second leakagemonitor further comprises a second differential amplifier connected to asecond branch of the second current mirror such that current through thesecond branch of the second current mirror mirrors current through theat least one P-type transistor, wherein the second differentialamplifier generates a second leakage current value.
 17. The method ofclaim 16, wherein the at least one class of N-type transistor includesmultiple threshold voltage types of N-type transistor, wherein the atleast one P-type transistor also includes multiple threshold voltagetypes of P-type transistor, wherein the first aggregating aggregates thefirst total device areas as a first set of device areas having memberscorresponding to a total device area of each of the N-type transistorsof the functional digital circuit the each of the multiple thresholdvoltage types of N-type transistor, wherein the second aggregatingaggregates the second total device areas as a second set of seconddevice areas having members corresponding to a total device area of eachof the P-type transistors of the functional digital circuit for each ofthe multiple threshold voltage types of P-type transistor, and whereinthe determining determines the design of the leakage current monitorcircuit such that the at least one N-type transistor comprises aplurality of N-type transistors, at least one for each of the multiplethreshold voltage types of N-type transistor and having device areasdetermined according to the first set of device areas, and such that theat least one P-type transistor comprises a plurality of P-typetransistors, at least one for each of the multiple threshold voltagetypes of P-type transistor and having device areas determined accordingto the second set of device areas.
 18. The method of claim 16, furthercomprising: first statistically modeling device area variation acrossthe integrated circuit to determine a nominal total area of the at leastone class of N-type transistor within the functional digital circuit;second statistically modeling device area variation across theintegrated circuit to determine is nominal total area of the at leastone class of P-type transistor within the functional digital circuit;first designing the device area of the at least one N-type transistor inthe leakage current monitor circuit in conformity with a result of thefirst statistically modeling; and second designing the device area ofthe at least one P-type transistor in the leakage current monitorcircuit in conformity with a result of the second statisticallymodeling.